The seasons

. As the Earth orbits the Sun, the Earthís rotational axis in a given hemisphere is tilted toward or away from the Sun. This variable tilt produces the seasons by changing the angle at which the Sunís rays strike different parts of the Earthís surface. The greatest sunward tilt occurs in the summer when the Sunís rays strike the surface most directly. In the winter, the relevant hemisphere is tilted away from the Sun and the Sunís rays obliquely strike the surface. When it is summer in the northern hemisphere, it is winter in the southern hemisphere and vice versa. (Notice that the radius of the Earth and Sun and the Earthís orbit are not drawn to scale.)